Chloroprene polymers containing a thio pyrimidine accelerator



United States Patent CHLOROPRENE POLYMERS CONTAINING A 'rrno PYRIMIDINE ACCELERATOR Jack C. Bacon, Noroton Heights, Conn., assignor to R. T. Vanderbilt Company, -Inc., New York, N.Y., a corporation of New York No Drawing, Filed Feb. 26, 1957, Ser. No. 642,368

8 Claims. (Cl. 260 -79.5)

The present invention relates to the vulcanization of chloroprene polymers containing a novel accelerator and especially to the vulcanization of the chloroprene polymer known as neoprene type W.

Chloroprene polymers or neoprene are polymers of 2-chloro-l,3-butadiene (chloroprene) and copolymers of chloroprene with dienes or vinyl compounds in which chloroprene comprises the predominant monomer. These polymers or copolymers are usually made in aqueous emulsions and are available to the rubber trade under such names as GR-M, neoprene type GN, neoprene type GNA, neoprene type FR, neoprene type B, neoprene type K, neoprene type KNR, neoprene type W, and neoprene type WRT. The various types of polychloroprene or neoprene differ one from the other in the modifier used in controlling the degree of polymerization of chloroprene, typical modifiers being sulfur, sulfur dioxide, hydrogen sulfide, mercaptans, iodine compounds and aromatic azo compounds. rently finding wide commercial acceptance because of its uniformity in molecular weight distribution and useful properties is neoprene type W, a stabilized chloroprene polymer containing no sulfur, thiuram disulfide, or other compound capable of decomposing to liberate free sulfur or form vulcanization accelerators.

Polychloroprenes differ greatly from other synthetic rubbers and from natural rubber in the manner in which they can be vulcanized. In general, excellent vulcanizates may be obtained from polychloroprenes by incorporating certain metallic oxides, such as zinc oxide and mag nesia, into the plastic polychloroprene and heating to effect vulcanization. For certain applications litharge is The chloroprene polymer which is cur- 2,943,078 Patented June 2 8, 196Q HCC will impart to the vulcanizates physical propertieswhich are comparable to those imparted by ethylenethiourea and which is less scorchy than ethylenethiourea, the best accelerator developed heretofore. It is a further object to provide an accelerator which is less expensive and easier, to prepare than is ,ethylenethiourea.

The accelerator of the present invention having these 7 desirable properties is a thio pyrimidine of the following recommended for use in place of the zinc oxide and magi nesia, while for some types sulfur is recommended but is not necessary to efiect vulcanization. Y

When a more rapid rate of cure is desired than can be obtained by the use of these metallic oxides alone, it has been the custom of the rubber trade to employ certain organic compounds as accelerators in conjunction with these metallic oxides. Thiocarbanilide or N,N'-diphenylthiourea is an example of an accelerator which has been used heretofore in the vulcanization of natural rubber, while catechol derivatives and 'hexamethylenetetramine are examples of previously 'used accelerators in the vulcanization of polychloroprene. The accelerator which has proved most efl ective up to this time in the vulcanization of polychloroprene is ethylenethiourea. The heretofore known accelerators, including those mentioned above, either do not impart to the vulcanizate the desired physical properties or are too scorchy, i.e., they are so active at relatively low temperatures that the poly structure and which canexist in two tautomeric forms as illustrated below.

CH; CH1.

I I H O N H1O N 11,0 H3O I \J /GSH H30 111 HaC N 2-thio-4,4,6-trimethyl 2-n1ercapto-4,4,6-trimethyl tetrahydro pyrimidine dihydro pyrimidine The accelerator may be prepared by the following inexpensive and easy classical method involving the reaction of an alpha,beta-unsaturated ketone with thioureaz- A further method for the preparation of the accelerator is set forth in Beilstein, volume 24, page 72. I

The amount of the accelerator which is incorporated in the chloroprene polymer stock may vary within-rather broad limits. In general, from about 0.05% to about 5.0% of the accelerator based on the weight of the chlo-' roprene polymer'is employed. It is preferred to use from about 0.5% to about 1.0% of the accelerator based on the weight of the chloroprene polymer present in the stock to be vulcanized.

The accelerator may be used' in conjunction with conventionalcompounding ingredients used in the preparation of polychloroprene vulcanizates. Typical examples of such ingredients include antioxidants, metallic oxides, colors, softeners and peptizers, fillers and extend ers, reinforcing materials and carbon blacks, and fatty acids and lubricants. I The invention will be further illustrated by the'data pertaining to Examples 1 through 4 below.

Typical polychloroprenes, namely neoprene type W or neoprene ty-pe WRT, were compounded by milling to- Silene .EF is a proprietary grade of finely divided calcium silicate. The polychloroprene stock was vulcanized by 7 press curing at 307 F. for varying lengths of time as set forth in the tables of the examples. The physical properties of the various vulcanizates, such as stress,

, tensile strength, elongation, and hardness wer measured.

as well as the Mooney scorch values. The accelerator of STRESS IN P.S.I. T N the invention, 1.e., 2-thio-4,4,6-trimethyl tetrahydro py- A 300% ELONGATIO rimidine, was compared with the best previously known 10 no 220 accelerator, namely ethylenethiourea. 15- 200 300 5 28 240 340 320 420 EXAMPLE 1 45 400 420 Formula A Components: Parts by weight TENSILE STRENGTH IN P.S.I.

Neoprene type W 100 Stearic acid 0.5 10 1 1,3 Zmc 3 20 11340 iliio Extra light calcined magnesium oxide 2 30 I, 500 1,500 Age Rite Stalite 2 45 11609 P-33 black 75 r Accelerator 0.5 PERCENT ELONGATION AT BREAK Table I 1,000 000 980 810 020 740 241110440 800 070 Press Cure in Minutes at 307 F. trimethyl Ethylene- 730 640 tetrahydro thiourea pyrimidine MOONEY SCORGH AT 250 F. (MINUTES TO 5 POINT RISE) 20 a 6 30 as 33 37 STRESS IN P.S.I. AT 300% ELONGATION 38 i223 i'fi 1' 510 1,740 EXAMPLE 3 45 1,590 1,830

Formula C TENSILE STRENGTH IN P.S.I.

Formula C is identical with Formula B in all respects w 2150 2,180 except that 0.25 part of sulfur was added. 20- 2, 350 2, s00 30 2, 480 2. 300 2, 480 2,450 TABLE 11 PERCENT ELONGATION AT BREAK 2-thio-4,4,0- Press Cure in Minutes at 307 F. trimethyl Ethylene- 10 630 550 tetra-hydro thlouren 520 400 pyrimidine 30. 480 490 45 400 470 MOONEY SCORCH A'I 250 F. (MINUTES To 5 POINT RISE SHORE HARDNESS N0. 45

10 57 00 20 00 62 30 00 03 STRESS IN P.S.I. AT 300% ELONGATION 4s 03 0 EXAMPLE 2 28!) 300 350 350 Formula B 400 400 Components: Parts by weight Neoprene tVP? W 55 TENSILE STRENGTH IN P.S.I. Neophax A 20 g Rlte Staht 0.5 0 1,210 L310 Petrolatum 1 1,300 Plasticizer sc 2s Hi3 Extra light calcined magnesium oxide 4 1,490 Thermax 25 Dixie clay 45 Zinc oxide 5 Accelerator 0.5 m 1, 000 m 200 $3 I i TABLE II 740 690 070 030 241110440- Press Cure in Minutes at 307 F. trimetliyl Ethylenetetrahydro thiourea SHORE HARDNESS NO. pyrimidine 25 30 MOONEY SOOROH AT 250 F. (MINUTES TO 5 POINT RISE) g I 1 as 30 26 10 41 42 EXAMPLE 4 Formula D Components: Parts by weight Neoprene type WRT 100 Age Rite Stalite 2 Petrolatum- 1 Circo light oil 10 Diethylene glycol 4 Silene EF 50 Zinc oxide 5 Extra light calcined magnesium oxide 4 Sulfur 0.25 Accelerator (as shown in Table IV TABLE IV trlmethyl Ethylene Press Cure in Minutes at 307 F. tetrahydro thlom-ea pyrimidine 0.5 part 0.75 part MOONEY SCOROH AT 250 F. (MINUTES To 5 POINT RISE) sTREss IN P.S.I. AT 300% ELONGATION TENSILE STRENGTH IN Per.

PERCENT ELONGATION. AT BREAK SHORE HARDNESS NO.

45 4s 47 49 so 51 52 52 From a study of the data in Tables I through IV above it may be readily seen that the accelerator of the invention, 2-thio-4,4,6 -trimethyl tetrahydro pyrimidine, cures a chloroprene polymer such as neoprene type W or neoprene type WRT. Moreover, the accelerator of the invention imparts to the vulcanizates physical properties comparable to those imparted thereto by ethylenethiourea, and most important, it is not nearly as scorchy as is ethylenethiourea as shown by the higher Mooney scorch value.

While the acceleratorof the invention is of particular interest in the vulcanization of the chloroprene polymer known as neoprene type W, it will be appreciated that it is useful in the vulcanization of other chloroprene polymers one of which has been shown in the examples above.

Various modifications and changes may be made in the invention herein set forth without departing from the spirit thereof and accordingly the invention is to be limited only within the scope of the appended claims.

I claim:

1. A vulcanizable polychloroprene composition free from undesirable scorchy properties comprising an unvulcanized chloroprene polymer and from about 0.05% to about 5.0% of the weight of the polymer of an accelerator which is 2-thio-4,4,6-trimethyl tetrahydro pyrimidine.

2. A vulcanizable polychloroprene composition tree from undesirable scorchy properties comprising an unvulcanized chloroprene polymer and from about 0.5% to about 1.0% of the weight of the polymer of an accelerator which is 2-thio-4,4,6-trimethyl tetrahydro pyrimidine.

3. A vulcanizable polychloroprene composition free from undesirable scorchy properties comprising a sulfurfree polychloroprene and from about 0.05 to about 5.0% of the weight of the polymer of an accelerator which is 2-thio-4,4,6-trimethyl tetrahydro pyrimidine.

4. A vulcanizable polychloroprene composition free from undesirable scorchy properties comprising a sulfurfree polychloroprene and from about 0.5 to about 1.0% of the weight of the polymer of an accelerator which is 2thio-4,4,6-trimethyl tetrahydro pyridimine.

5. The process of vulcanizing chloroprene polymers comprising incorporating in a chloroprene polymer stock from about 0.05 to about 5.0% of the weight of the polymer of an accelerator which is 2-thio-4,4,6-trimethyl tetrahydro pyrimidine and heating at vulcanizing temperatures to cure the polymer.

6. The process of vulcanizing chloroprene polymers comprising incorporating in a chloroprene polymer stock from about 0.5% to about 1.0% of the weight of the polymer of an accelerator which is 2-thio-4,4,6-trimethy1 tetrahydro pyrimidine and heating at vulcanizing temperatures to cure the polymer.

7. The process of vulcanizing chloroprene polymers comprising incorporating in a sulfur-free polychloroprene stock from about 0.05 to about 5.0% of the weight of the polymer of an accelerator which is 2-thio-4,4,6-trimethyl tetrahydro pyrimidine and heating at vulcanizing temperatures to cure the polymer.

8. The process of vulcanizing chloroprene polymers comprising incorporating in a sulfur-free polychloroprene stock from about 0.5% to about 1.0% of the weight of the polymer of an accelerator which is 2-thio-4,4,6-trimethyl tetrahydro pyrimidine and heating at vulcanizing temperatures to cure the polymer.

References Cited in the file of this patent UNITED STATES PATENTS 2,234,848 Ter Horst Mar. 11, 1941 2,525,200 Bergmann 'Oct. 10, 1950 2,544,746 Baum Mar. 13, 1951 OTHER REFERENCES Beilstein: vol. 24, p. 72 (1936). (Copy in Library.) 

1. A VULCANIZABLE POLYCHLOROPRENE COMPOSITION FREE FROM UNDESIRABLE SCORCHY PROPERTIES COMPRISING AN UNVULCANIZED CHLOROPRENE POLYMER AND FROM ABOUT 0.05% TO ABOUT 5.0% OF THE WEIGHT OF THE POLYMER OF AN ACCELERATOR WHICH IS 2-THIO-4,4,6-TRIMETHYL TETRAHYDRO PYRIMIDINE. 